This application requests support for a program of basic and clinical research on speech perception and spoken word recognition. The primary objective of this project is to understand how spoken words are recognized and how acoustic-phonetic and indexical information in the speech signal interact with other knowledge sources to support robust spoken language understanding. The proposed research will involve behavioral studies of speech perception and spoken word recognition as well as computational analyses of the sound patterns of word-forms in the mental lexicon to study global organization and connectivity patterns of spoken words. Four specific aims will be studied: (1) lexical knowledge and organization, (2) perceptual learning and adaptation, (3) speech perception under adverse listening conditions, and (4) individual differences in working memory dynamics (capacity and speed) in hearing-impaired listeners with cochlear implants (CIs). The research findings will provide a much stronger conceptual and theoretical basis for explaining the core underlying factors that are responsible for the variability and individual differences observed in speech and language processing in normal-hearing typical-developing listeners. The results from this project will also have important direct clinical implications for understanding individual differences in speech and language outcomes in hearing-impaired children and adults who use CIs.